ANGE POSTECOGLOU has told his Celtic players he expects a reaction to their 4-0 thumping at the hands of Bayer Leverkusen, and says that they have to be mentally stronger if they are going to succeed at the club.

The Celtic manager was hugely disappointed by aspects of his team’s play in their second Europa League group stage defeat in a row, and was particularly upset by their weakness in conceding a fourth goal on the night.

He is now demanding that they show a massive improvement in Sunday’s huge Premiership encounter against Aberdeen at Pittodrie.

“It has to happen soon,” Postecoglou said. “I’m disappointed for our fans tonight.

“They created a great atmosphere and we had such a good start to the game, we really took it to them and created several opportunities.

“So to walk away tonight losing 4-0, we’re all very disappointed in the dressing room - and we should be. We need to have a reaction.

“We’ve made things difficult for ourselves, even towards the end there was no need to concede a fourth. It shouldn’t have been a 4-0 game. We’ve got to be stronger mentally and keep ourselves in the game.

“It’s one thing me being supportive but there’s got to be a reaction to this. We’ve just got to keep persevering.

“We’ve had a number of injuries, we’ve rebuilt the squad - all those kind of things - it’[s not surprising it’s taking time. But I still feel even within that we can be better.

“We’ve just got to persevere and push through it, use the disappointment we have to fuel some fire to turn things around.”

Postecoglou again bemoaned the lack of a ruthless edge at both ends as the factor that is currently killing his team.

“We had some great chances and it’s a story of both boxes,” he said. “They’re a good side, they were clinical in the box.

“We made some mistakes that you can’t make at this level, so it was disappointing overall.

“I still think we had a couple of moments we could’ve done better in, although to be fair, their keeper’s pulled off some unbelievable saves as well.”